1. The Field of the Invention
The invention relates to a composite to metal joint for torsional shafts.
2. Description of the Prior Art
The use of composite fibers rather than metal for a torsional shaft, such as the drive shaft of an automobile, van or pickup truck, is desirable for many reasons, including for weight reduction, corrosion resistance, durability, and increased strength. However, even when a composite fiber is used as a torsional shaft, an end of the shaft must still be coupled to a metal at a joint that can withstand the torsional and other stresses that will exist during transfer of the load by rotation of the shaft. It is this joint that is usually the weakest point of the torsional shaft.
The use of adhesives has been attempted to increase the strength and durability of the joint, such as that described in U.S. Pat. No. 4,664,644, but the load transfer is entirely due to the adhesive. Pins in the form of bolts or rivets have also been used to increase the strength and durability of the joint, but such pins require drilling holes in both the metal and the composite, which tend to weaken the composite at the joint, and their usage substantially increases manufacturing expenses.
U.S. Pat. No. 4,358,284 describes using a metal at the joint having projections or depressions, such as grooves, bumps or flutes, providing a form locking connection at the joint, but such patent does not further specify the geometry of the projections that will accomplish this form locking connection.
One specific geometry proposed that will form a locking connection at the joint is disclosed in U.S. Pat. No. 4,236,386. As shown in FIG. 3 of the patent, the disclosed locking geometry of the metal has a cross section that consists of numerous out-of-plane flat surfaces with sharp angles between each flat surface. However, when filament winding the fibers over the flat sections of the metal, the radial component of fiber tension cannot be kept across the whole flat section, the requisite compaction of fibers cannot be kept, and voids will occur. Furthermore, the fiber path across the flat sections cannot be predicted with certainty.